全文获取类型
收费全文 | 169939篇 |
免费 | 2019篇 |
国内免费 | 536篇 |
专业分类
化学 | 95880篇 |
晶体学 | 2494篇 |
力学 | 6613篇 |
综合类 | 3篇 |
数学 | 17822篇 |
物理学 | 49682篇 |
出版年
2021年 | 1265篇 |
2020年 | 1462篇 |
2019年 | 1548篇 |
2018年 | 1859篇 |
2017年 | 1874篇 |
2016年 | 3007篇 |
2015年 | 1990篇 |
2014年 | 2823篇 |
2013年 | 7283篇 |
2012年 | 5896篇 |
2011年 | 7277篇 |
2010年 | 4867篇 |
2009年 | 4883篇 |
2008年 | 6919篇 |
2007年 | 6704篇 |
2006年 | 6541篇 |
2005年 | 6072篇 |
2004年 | 5421篇 |
2003年 | 4966篇 |
2002年 | 4774篇 |
2001年 | 5867篇 |
2000年 | 4236篇 |
1999年 | 3306篇 |
1998年 | 2375篇 |
1997年 | 2503篇 |
1996年 | 2403篇 |
1995年 | 2146篇 |
1994年 | 2186篇 |
1993年 | 1975篇 |
1992年 | 2441篇 |
1991年 | 2527篇 |
1990年 | 2313篇 |
1989年 | 2326篇 |
1988年 | 2301篇 |
1987年 | 2275篇 |
1986年 | 2097篇 |
1985年 | 2648篇 |
1984年 | 2717篇 |
1983年 | 2114篇 |
1982年 | 2262篇 |
1981年 | 2078篇 |
1980年 | 2036篇 |
1979年 | 2333篇 |
1978年 | 2409篇 |
1977年 | 2331篇 |
1976年 | 2239篇 |
1975年 | 2093篇 |
1974年 | 2073篇 |
1973年 | 2100篇 |
1972年 | 1357篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
The occurrence and formation of black spots areas in PolyLED devices has been studied by time-of-flight SIMS (TOFSIMS). The composition, shape and position of the black spots is visualised by three-dimensional (3D)-TOFSIMS depth-profiling. It has been established that the formation of non-emissive spots is due to the growth of aluminium oxide clusters at the AlBa/polymer interface. Electron injection in the black spots is lost by the resulting local increase of the resistivity of the cathode. 相似文献
73.
Photoisomerization of provitamin D 3 (7-dehydrocholesterol) in a nematic liquid crystal (ZLI-1695, Merck) is investigated in detail by UV absorption spectroscopy. It is found that dissolution of chiral molecules of provitamin D 3 induces the cholesteric phase in a nematic. The spectral kinetics of photoisomerization in this phase changes significantly from that in an ethanol solution. A sharp nonmonotonic dependence of the increase in accumulation of trans isomer tachysterol in a liquid crystal matrix with a decrease in the induced cholesteric pitch from 2200 to 25 μm is revealed. 相似文献
74.
Evstafyeva I. T. Bozhenkov G. V. Aizina Ya. A. Rozenzveig I. B. Ermakova T. G. Levkovskaya G. G. Mirskova A. N. 《Russian Journal of Organic Chemistry》2002,38(8):1178-1182
1H-Pyrazoles, triazoles, and imidazoles in reaction with ethoxycarbonylimine and arylsulfonylimines of chloral yield addition products, corresponding 1-(1-amidotrichloroethyl)azoles. Derivatives of 1-alkylpyrazoles and pyrazolones react with chloral 4-chlorophenylsulfonylimine to furnish products of C-amidotrichloroethylation into position 4 of the azole ring. 相似文献
75.
The spin-1 Ising model, which is equivalent to the three-component lattice gas model, is used to study wetting transitions in three-component surfactant systems consisting of an oil, water, and a nonionic surfactant. Phase equilibria, interfacial profiles, and interfacial tensions for three-phase equilibrium are determined in mean field approximation, for a wide range of temperature and interaction parameters. Surfactant interaction parameters are found to strongly influence interfacial tensions, reducing them in some cases to ultralow values. Interfacial tensions are used to determine whether the middle phase, rich in surfactant, wets or does not wet the interface between the oil-rich and water-rich phases. By varying temperature and interaction parameters, a wetting transition is located and found to be of the first order. Comparison is made with recent experimental results on wetting transitions in ternary surfactant systems.This paper is dedicated to J. K. Percus in honor of his 65th birthday. 相似文献
76.
Summary In this paper a Gauss-Jordan algorithm with column interchanges is presented and analysed. We show that, in contrast with Gaussian elimination, the Gauss-Jordan algorithm has essentially differing properties when using column interchanges instead of row interchanges for improving the numerical stability. For solutions obtained by Gauss-Jordan with column interchanges, a more satisfactory bound for the residual norm can be given. The analysis gives theoretical evidence that the algorithm yields numerical solutions as good as those obtained by Gaussian elimination and that, in most practical situations, the residuals are equally small. This is confirmed by numerical experiments. Moreover, timing experiments on a Cyber 205 vector computer show that the algorithm presented has good vectorisation properties. 相似文献
77.
In this paper, we show that in some cases, no proper covering of a locally compact group topologically generated by left translations
of a topological loop can occur as the group topologically generated by left translations of a topological loop.
__________
Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 22, Algebra
and Geometry, 2004. 相似文献
78.
S. K. Godunov V. T. Zhukov O. B. Feodoritova 《Computational Mathematics and Mathematical Physics》2006,46(6):971-982
An algorithm is constructed for calculating invariant subspaces of symmetric hyperbolic systems arising in electromagnetic, acoustic, and elasticity problems. Discrete approximations are calculated for subspaces that correspond to minimal eigenvalues and smooth eigenfunctions. Difficulties related to the presence of an infinite-dimensional kernel in the differential operator are successfully handled. The efficiency of the algorithm is demonstrated using acoustics equations. 相似文献
79.
Robert de Levie 《The Chemical Educator》2002,7(3):132-135
Using contemporary accounts, we describe the scope of the Henderson approximation, and its relationship to the mass action law of Guldberg & Waage. The Henderson approximation, apparently written in logarithmic form by Hasselbalch, has the same form as the mass action law, but has a completely different meaning and a much more restricted range of applicability. The Guldberg-Waage law is the fundamental mass action relationship valid for all chemical equilibria, whereas the Henderson approximation is useful only within a limited range of a sufficiently concentrated two-component buffer mixture. 相似文献
80.